Illumination device and method for illuminating an object

ABSTRACT

The invention relates to an illumination device for illuminating an object to be measured, especially defined for a co-ordinate measuring device or a measuring microscope. Said device comprises a plurality of light sources stemming from a holding element ( 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 ). Said light sources have various angles of incidence in relation to an optical axis ( 14 ) of an optical instrument, by which means the object can be measured or reproduced. In order to be able to adjust the illumination on various working planes without using a complex mechanism, in order to illuminate an object to be measured or a surface or an edge thereof in an optimum manner, light sources ( 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 ) are arranged in the holding element ( 16 ) in such a way that the angles of incidence thereof cut the optical axis ( 14 ) in the region of working intervals ( 48, 50, 52, 54, 56 ) of the optical instrument, said intervals deviating from each other.

[0001] The invention concerns an illumination arrangement forilluminating an object to be measured, destined in particular for acoordinate measuring device or a measuring microscope, comprisingseveral light sources extending from a support and having differentincidence angles with respect to an optical axis of an optic with whichthe object can be measured or imaged. The invention also concerns aprocess for illuminating an object having several light sources withdivergent incidence angles with respect to an optical axis of an optic,with which the object is measured or imaged.

[0002] When using optical and multisensor coordinate measuring devicesas well as measuring microscopes, it is necessary to illuminate theobjects to be measured by means of suitable illumination arrangements.In these, the usual types of illumination are transmitted light, brightfield incident light and dark field incident light. By selecting betweenthe different illumination possibilities in dependence upon the shape ofthe object to be measured is ensured an optimal illumination. Thus, indark field illumination, only the light that is diffracted in the objectcontributes to the imaging, whereby individual structures appear brighton a dark background. In bright field illumination, the light to beemitted reaches directly into the object as transmitted light orincident light. The objects appear thus, insofar as they are themselvesrich in contrast, dark or colored on a bright background.

[0003] Of particular importance is the configuration of the dark fieldincident illumination. Herein are used systems in the form of, forexample, glass fiber ring lights or ring-shaped arrangements of LEDs(light-transmitting diodes). To be able to displace the illuminationangle within an unchanged working plane, the glass fiber ring lights aredivided into several segments or, to achieve the same results, the LEDareas can be connected and disconnected segment by segment. Because ofthis, there exists the possibility of exposing the object to be measuredto different lighting or to change the direction of incidence of thelighting.

[0004] Also known are proposals in which the angle between the surfaceof the object to be measured and the illumination incidence beam can beconfigured differently by means of a simultaneous lifting and loweringof an illumination source or spherical arrangement of severalillumination sources. It is disadvantageous of these measures thatcollision problems with the object to be measured can occur due to thenecessary mechanical displacement of the illumination system. Arelatively complicated mechanism becomes necessary or the entire workingdistance is unfavorably reduced.

[0005] From DE 39 06 555 A1 an incident light object illumination devicewith selectable light incidence angle and several individuallyswitchable light sources is known. At the same time, an illumination atdifferent selectable illumination angles is possible without amechanical displacement of the light sources or imaging elements, and atthe same time, an illumination at different selectable illuminationangles. For this purpose, the light sources going out from acalotte-shaped support, which can be arranged concentrically around atube of a microscope, can all be aligned with respect to an objectplane, so that the imaging distance is to be selected always equal. Anarrangement for this purpose is also conceivable for coordinatemeasuring apparatuses.

[0006] In a programmable surface illuminator for video testing devicesaccording to DE 199 04 899 A1, LEDs aligned parallel to each other goout from a disk-shaped support whose beams fall on a parabolic mirror,by means of which the radiation can fall on the object to be measured atincidence angles within a range between 45° and 90°.

[0007] It is also known to arrange a Fresnel lens between light sourcessuch as light-emitting diodes and an object to be measured so as toilluminate an object to be measured at different incidence angles (DE198 37 797 A1).

[0008] Other arrangements for illuminating an object at divergentincidence angles focused on a mutual working plane are disclosed in U.S.Pat. No. 4,893,223 or DE 196 53 234 A1.

[0009] From DE 40 16 264 C2 is known a fiberoptic multi-point lamp witha cylinder-shaped head for illuminating the working field of amicroscope.

[0010] To adjust the illumination of a fiberoptic multi-point lamp to adesired object field, light conducting fiber bundles are configured soas to be movable according to DE 32 00 938 A1.

[0011] It is an object of the invention to further develop anillumination arrangement as well as a process for illuminating an objectin such a way that a problem-free adjustment of the illumination ispossible within different working planes so as to optimally illuminatean object to be measured or a surface or edge of the object. Alimitation of the measuring range should at the same time not take placedue to the light sources themselves.

[0012] The object is attained according to the invention essentially bymeans of an illumination arrangement of the kind described above byarranging the light sources in such a way within a support that theirincidence angles intersect the optical axis within areas, which arespaced with respect to each other, in particular within divergentworking distances of the optic. It is provided especially that the lightsources on the optical axis are preferably arranged on concentricallysurrounding circles, while the light sources arranged on circles ofdifferent diameters can intersect the optical axis in areas havingdivergent working distances.

[0013] The support for the light sources can span a plane thatvertically intersects the optical axis. The support can therein form acircular disk or can also consist of only one or several cubic orbeam-shaped holders for the light sources.

[0014] There is also the possibility of configuring the support in theshape of a hood or calotte that in turn surrounds concentrically theoptical axis.

[0015] To make possible a high density of the light sources to bemounted, the invention provides that the light sources such as LEDs arearranged radially offset with respect to each other on successivecircles.

[0016] The support having the desired geometry should have recesses suchas bores, in which the light sources can be preferably fixedly arranged.However, there is also the possibility of displacing as well as pivotingthe light sources themselves in the individual recesses.

[0017] It is especially provided that the support is in itselfvertically adjustable, that is, it is configured so as to bedisplaceable along the optical axis. Such an arrangement is suitable inparticular for a measuring arrangement with an optic, which has aconstant or essentially constant working distance.

[0018] In a support with a calotte or hood-shaped geometry, the sameshould have at its object side an area for accommodating the lightsources with a radius of curvature of 40 mm≦R≦80 mm, in particular R ofabout 60 mm. Through this, the light sources can be arranged in such away in particular on circles running concentrically with respect to eachother, that the beams intersect the working plane at an angle of 50 toup to, for example, 85°, without the support having to have a heightthat causes the danger of a collision with the object to be measured. Atthe same time, it is not required that the support be displaced withrespect to the optic or the housing wherein it is accommodated.

[0019] An angular adjustment between the illumination beam and thesurface of the object can take place according to the invention by meansof different angular positions of fixedly arranged light sources,wherein these are arranged within a plane that is located in acollision-free space. In dependence upon the effective working distanceor area to be illuminated are used those light sources whose angularpositions are aligned with respect to the working distance or operatingrange. Vice versa, the angular displacement is achieved by changing theeffective working distance of the used optic or the optical system. Ofcourse, there is also the possibility of utilizing always all oressentially all of the light sources to illuminate the object, whereinalways an optimal illumination of the object takes place on the workingplane, since in accordance with the invention groups of light sourcesintersect the optical axis of the optic in different areas or sections.Consequently, in this case, the work can be carried out withoutadditional mechanical displacement at different illumination incidenceangles as well as also sufficiently long working distances.

[0020] If the illumination arrangement of the invention is destined inparticular for dark field incident light processes, then it is possibleto use the arrangement also for bright field incidence measurementswithout problems. For this purpose, it is provided that the radiationemitted by the light sources is deflected in such a way that these meetalong the optical axis on the object. Of course, the imaging optic canalso be provided in the usual way for a bright field incident lightarrangement.

[0021] If, as mentioned, the light sources are preferably LEDs, thenalso fiber bundles and/or fiber ring segments can be used to realize theteaching of the invention. As light sources are also suitable, however,mirrors by means of which the light can be deflected in such a way thatthe incidence angles of the radiations reflected by the mirrorsintersect the optical axis of the optic in divergent areas, inparticular working distances.

[0022] In a further development, it is provided that the optic comprisesseveral cameras provided at different distances between the lens vertexand the back focus, to which is assigned a mutual objective with fixedfocal distance. The optic can also comprise several objective-camerasystems, which have divergent working distances with respect to theobject.

[0023] Independently thereof, the optic can be configured as zoom opticwith a variable working distance, that is, it can have a design as seenin WO 99/53268, to whose disclosure is made reference expressly herein.

[0024] The light sources can also illuminate the object with divergentcolors, wherein, if required, light sources with an identical incidenceangle illuminate the object with the same color.

[0025] A process for illuminating an object with several light sourceshaving divergent incidence angles with respect to an optical axis of anoptics mechanism, with which the object is measured or imaged, ischaracterized in that the incidence angle of the light sources isaligned in such a way with respect to the optical axis that differentlight sources intersect the optical axis in areas, which are spaced withrespect to each other. At the same time, the object can be illuminatedwith the light sources whose incident angles are aligned in dependenceupon the working distance. There is also the possibility of adjustingthe working distance of the optic in dependence upon the incidence angleof one of the light sources that illuminate an area of the object to bemeasured.

[0026] Finally, a support that accommodates the light sources can bedisplaced along the optical axis with a fixed working distance of theoptic so as to illuminates the object with desired incidence angle.

[0027] Further details, advantages, and features of the invention do notresult only from the claims, the features disclosed therein, per seand/or in combination, but also from the following description of thepreferred exemplary designs seen in the drawings.

[0028] In the drawings,

[0029]FIG. 1 shows a schematic diagram of an illumination arrangement ofan optical measuring device,

[0030]FIG. 2 shows in sectional view a support for the illuminationarrangement according to FIG. 1,

[0031]FIG. 3 shows an alternative design of the illumination arrangementof FIG. 1, and

[0032]FIG. 4 shows a schematic diagram of another design of anillumination arrangement.

[0033] In FIG. 1 is shown a section view and a cutout of an opticalmeasuring device 10 with a housing 12 wherein the optic is accommodated,which is not shown, by means of which a radiation reflected by an objectto be measured is imaged in a camera such as a CCD camera. The optic canbe configured therein as zoom optic with a variable working distance,whose lens groups can be displaced independently from one other asdisclosed in WO 99/53268. This optical measuring device 10 can be inparticular part of a coordinate measuring system.

[0034] A support 16 is arranged concentrically with respect to theoptical axis 14 of the optic, in which light sources, preferably in theform of LEDs, are arranged on circles running concentrically toward eachother and radially offset with respect to each other. In the sectionview according to FIG. 1, the LEDs 18, 20 are arranged on a firstcircle, the LEDs 22, 24 are arranged on a second circle, the LEDs 26, 28are arranged on a third circle, the LEDs 30, 32 are arranged on a fourthcircle, and the LEDs 34, 36 are arranged on a fifth circle.

[0035] For this purpose, the support 16 has holders 38, 40, 42, 44, and46 arranged on circles running concentrically toward each other for theLEDs 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36, wherein these arearranged in such a way in the holders 38, 40, 42, 44, and 46 thatdifferent incidence angles result with respect to the optical axis 14.In this way, for example, the openings 38 are arranged on a circle onwhich the LEDs enclose an incidence angle α of approx. 70° with respectto the optical axis 14. By means of the openings 40 arranged on acircle, the LEDs are aligned at an angle β of, for example, 35° withrespect to the optical axis 14. Concerning the openings 42 can be presetan angle γ of about 100. The openings 44 lie again on a circle runningconcentrically with respect to the optical axis so as to intersect theLEDs at an incidence angle δ of, for example, 25°. Regarding theopenings 46 can result, for example, an angle κ of 50°, while thedisclosed values are mentioned purely as examples.

[0036] By means of the previously mentioned configuration of the support16 it is achieved that the LEDs 18, 20, 22, 22, 24, 26, 28, 30, 32, 34,and 36 arranged on the circles running concentrically with respect toeach other, which are represented by the holders 38, 40, 42, 44, and 46,intersect the optical axis 14 at different incidence angles inoperational ranges, which are spaced with respect to each other, whichare illuminated along the optical axis 14, and which are designated withthe reference numerals 48, 50, 52, 54, and 56 in FIG. 1.

[0037] If, for example, a surface to be measured or an edge of an objectis located within the operational range or within the working plane 52,then the light diodes 26, 28 are used, which illuminate optimally theworking plane 52. If the working distance is changed, for example, bydisplacing the working distance within the plane 54, are then insteadoptimally active the light diodes 30, 32. Thus, it can be optimallymeasured over a large working distance range without requiring amechanical displacement of the LEDs 18, 20, 22, 24, 26, 28, 30, 32, 34,and 36 or the support 16 with respect F to the housing 12 thataccommodates the optic.

[0038] The light sources are always aligned in such a way with respectto each other, that their beams meet within a predetermined workingplane or illuminate a corresponding working plane. This again means thatan area to be measured is always aligned with respect to thecorresponding working plane.

[0039] Because in the illumination arrangement of the invention, theLEDs 18, 20, 22, 24, 26, 28, 30, 32, 34, are arranged on rings thatconcentrically enclose the optical axis 14 at defined angles indifferent sections of the optical axis 14, these are focused on anotherpoint of the optical axis 14 of the optic, that is, in the exemplarydesign of FIG. 1 they are focused on the intercept points between theoptical axis 14 and the operational ranges or working planes 48, 50, 52,54, and 56. While the focusing of the imaging system, that is, whilefocusing the optic on the corresponding intercept point, is produced adifferent beaming angle between the illumination angle and the surfaceof the object to be measured, so that an optimal illumination andconsequently a high quality measurement is ensured.

[0040] As clarified in particular in FIG. 2, the height of the support16 is relatively low notwithstanding the possibility that by means ofthe light diodes 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36 can beobtained incidence angles with respect to the axis 14 within the rangebetween 5° and 850 or more, and thus a correspondingly long operationalrange is made available, within which measurements can be carried out,so that the danger of collisions with an object to be measured areprecluded.

[0041] For this purpose, it is especially provided that the surface 58of the support 16 on the object side has a curvature radius R especiallywithin a range between 30-90 mm, preferably 50-70 mm. As a consequenceof the curvature radius R, the diameter of the support 16 itself isrelatively small, whereas the inner diameter amounts to a maximum of 4to 5 times the minimal working distance between the free lower side ofthe support 16 and an object to be measured. Thus, the distance betweenthe light diodes 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36 and theobject to be measured is relatively small, so that again a high lightingis ensured.

[0042] While measuring, an object can be moved within the operationalrange in which an optimal illumination takes place. In dependence uponthe light sources used until now can then be automatically adjusted theworking distance of the measuring optic. There is in contrast thepossibility of adjusting the optic without problem to a specific workingdistance, wherein the light sources, which are aligned with respect tothis working distance, are switched on in dependence upon the workingdistance.

[0043] Furthermore, in the schematic diagram of FIG. 1 it can be seenthat along the optical axis 14 can be imaged a bright field incidentradiation by means of optical deflecting elements 58, 60.

[0044] The design in FIG. 3 differs from the one in FIG. 1 to the effectthat the support does not have a hood or calotte-shaped geometry withrespect to the arrangement of the light sources 18, 20, 22, 24, 26, 28,30, 32, 34, and 36, but rather a rod or disk-shaped geometry, in whichthe light sources 18, 20, 22, 24, 26, 28, 30, 32, 34, and 36 arearranged within a plane, which preferably intersects vertically theoptical axis 14.

[0045] If the support 16 is preferably basically a dial, whichconcentrically encloses the optic, then the light diodes 18, 22, 26, 30,and 34, on the one hand, and 20, 24, 28, 32, and 36, on the other hand,can be arranged alternatively within the cube or beam-shaped holders,which run parallel to each other.

[0046] If in the exemplary design of FIGS. 1 and 2 is provided asupport, which has the sphere or calotte-shaped geometry with respect tothe holders or arrangements of the light sources, then there is also thepossibility according to FIG. 4 (as well as according to FIG. 3) ofarranging the light sources 60, 62, 64, 66, and 68 at differentincidence angles, which intersect the optical axis in areas, which arespaced with respect to each other. The light sources 60, 62, 64, 66, and68 can be arranged in cubical or beam-shaped holders as the support 70,which in turn span a plane that runs especially vertical to the opticalaxis. A ring arrangement can also be selected, wherein the correspondingsupport can form a disk. The light sources 60, 63, 64, 66, and 68 canthus be arranged within a mutual plane, which runs parallel to the planespanned by the support 70. To be able to illuminate the object 72 atdifferent incidence angles, it is therefore necessary that the support70 be displaced along the optical axis, that is, in accordance with thedouble arrow 74. In dependence upon the position of the support 70,light sources 60, 62, 64, 66, and 68 are activated at differentincidence angles, whereby the object 72 is illuminated at differentangles. This is clarified purely on principle in view of FIG. 4.

[0047] Regardless of this, the arrangement of FIG. 4 obeys the teachingof the invention insofar as, if the support 70 is fixedly arranged, theaxes of the light sources 60, 62, 64, 66, and 68 intersect the opticalaxis in areas, which are spaced with respect to each other.

1. An illumination arrangement for illuminating an object to bemeasured, destined in particular for a coordinate measuring system or ameasuring microscope, comprising several light sources (18, 20, 22, 24,26, 28, 30, 32, 34, 36, 60, 62, 64, 66, 68) going out from a support(16, 70) having different incidence angles with respect to an opticalaxis (14) of an optic, by means of which the object can be measured orimaged, wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32, 34,36, 60, 62, 64, 66, 68) in the support (16, 70) are arranged in such away, that their incidence angles (a, P, y, 6, K) intersect the opticalaxis (14) in divergent areas (48, 50, 52, 54, 56).
 2. The illuminationarrangement of claim 1, wherein the incidence angles (a, P, y, 6, K)intersect the optical axis (14) at working distances (48, 50, 52, 54,56) of the optic which diverge from the areas.
 3. The illuminationarrangement of claim 1 or 2, wherein the light sources (18, 20, 22, 24,26, 28, 30, 32; 34, 36) are arranged on circles concentrically, whichenclose the optical axis (14), while the light sources (18, 20, 22, 24,26, 28, 30, 32, 34, 36) arranged on circles of different diametersintersect the optical axis (14) in divergent areas (48, 50, 52, 54, 56).4. The illumination arrangement of at least one of the previous claims,wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36),especially LEDs, are arranged on mutually successive circles, which areradially offset with respect to each other.
 5. The illuminationarrangement of at least one of the previous claims, wherein the support(16) encloses the optical axis (14) concentrically and in acollision-free way with respect to the object to be measured.
 6. Theillumination arrangement of at least one of the previous claims, whereinthe holder (16) for the light sources (18, 20, 22, 24, 26, 28, 30, 32,34, 36) has a hood or calotte-shaped geometry with recesses such asbores (38, 40, 42, 44, 46), in which the light sources are arranged. 7.The illumination arrangement of at least one of the previous claims,wherein the support (70) accommodates the light sources (60, 62, 64, 66,68) within a plane that intersects the optical axis preferablyvertically.
 8. The illumination arrangement of at least one of theprevious claims, wherein the support (72) has a disk-shaped geometrysuch as a dial-shaped geometry.
 9. The illumination arrangement of atleast one of the previous claims, wherein the support has a cubic orblock-shaped geometry.
 10. The illumination arrangement of at least oneof the previous claims, wherein the support consists of cubic orblock-shaped sections running diametrically to the optical axis (14).11. The illumination arrangement of at least one of the previous claims,wherein the support (70) is configured so as to be verticallydisplaceable.
 12. The illumination arrangement of at least one of theprevious claims, wherein the support (70) can be displaced manually orautomatically parallel to the optical axis.
 13. The illuminationarrangement of at least one of the previous claims, wherein, if theworking distance of the optic is constant, the object (72) can beilluminated by displacing the support (70) along the optical axis (14)at different light incidence angles.
 14. The illumination arrangement ofat least one of the previous claims, wherein the support (16) has on theside of the object a curvature radius R of 40 mm≦R≦80 mm, in particularR of about 60 mm.
 15. The illumination arrangement of at least one ofthe previous claims, wherein the radiation emitted by the light sources(18, 20, 22, 24, 26, 28, 30, 32, 34, 36) is deflected in such a way,that the object can be illuminated in the bright field incident light.16. The illumination arrangement of at least one of the previous claims,wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36) canbe arranged so as to be displaceable within the holders (38, 40, 42, 44,46) of the support (16).
 17. The illumination arrangement of at leastone of the previous claims, wherein the light sources (18, 20, 22, 24,26, 28, 30, 32, 34, 36) are arranged so as to be fixed within thesupport (16).
 18. The illumination arrangement of at least one of theprevious claims, wherein the light sources (18, 20, 22, 24, 26, 28, 30,32, 34, 36) are aligned fiber bundles and/or fiber ring segments. 19.The illumination arrangement of at least one of the previous claims,wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36) areradiations reflected by the mirrors.
 20. The illumination arrangement ofat least one of the previous claims, wherein the optic is a zoom opticwith variable working distance.
 21. The illumination arrangement of atleast one of the previous claims, wherein the optic comprises severalobjective-camera systems having divergent working distances with respectto the object.
 22. The illumination arrangement of at least one of theprevious claims, wherein the optic comprises several cameras indifferent distances between the lens vertex and the back focus, to whichis assigned a mutual objective with fixed focal distance.
 23. Theillumination arrangement of at least one of the previous claims, whereina bright field incident radiation can be mirrored along the optical axis(14).
 24. The illumination arrangement of at least one of the previousclaims, wherein the light sources (18, 20, 22, 24, 26, 28, 30, 32, 34,36) illuminate the object with divergent colors.
 25. The illuminationarrangement of at least one of the previous claims, wherein the lightsources (18, 20, 22, 24, 26, 28, 30, 32, 34, 36) with the same incidenceangles (α, β, γ, δ, κ) illuminate the object with the same color.
 26. Aprocess for illuminating an object with several light sources havingdivergent incidence angles with respect to an optical axis of an optic,with which the object is measured or imaged, wherein the incidence angleof the light sources is aligned in such a way with respect to theoptical axis that different light sources intersect the optical axis inareas, which are spaced with respect to each other.
 27. The process ofclaim 26, wherein if the working distance of the optic is fixed, thesupport is displaced along the optical axis to illuminate the object atdifferent incidence angles.
 28. The process of claim 26 or 27, whereinthe light sources, whose incidence angle are aligned toward the workingdistance, illuminate the object in dependence upon the working distanceof the optic.
 29. The process of one of the claims 26 to 28, wherein theworking distance of the optic is adjusted in dependence upon theincidence angle of the light sources that illuminate the object.